In my parent patent application Ser. No. 07/499,100, filed Mar. 26, 1990, and my U.S. Pat. Nos. 5,092,512 issued Mar. 3, 1992, and 5,104,026 issued Apr. 14, 1992, I disclose an automotive bumper and a method and apparatus of making such bumper of high strength steel and roll-formed into a tubular cross-section. As set forth in such application and patents, the inventions of the above said application and patents solve the problems by roll-forming a closed tubular cross-section from high strength sheet steel of at least 60 KSI and 0.100 inches maximum thickness. The forming of a closed section greatly increases the strength of the bar and allowed weight reduction by use of a reduced material thickness. The closed design also improved deflection curves by avoiding the sudden collapse experienced by traditional "C" section bumpers as the flanges gave way.
Another important aspect of those inventions is the formation of a sweep during the roll-forming process. Such sweep allows for manufacture of a bumper which will satisfy modern aerodynamic designs and also increase the strength of the bumper and improve its spring-back characteristics.
Although the bumper of the above said application and patents is a great improvement over the prior art, I have conceived of an improvement thereof which has even greater strength. In addition to the strength, it has the advantage of less cost and less weight than other prior art bumpers of similar shape such as disclosed in FIG. 14 which will be described hereinafter.
Another prior art reinforcement bar utilized in a front bumper is disclosed in FIG. 14 which discloses a W-shaped or so-called double hat shaped bumper having openings 4 and 5 covered by steel plate member 6 welded to the outer legs 7 and 8 of sections 1 and 2 and to the web 3.
The W-shaped bumper of FIG. 14 is formed by roll-forming a single sheet of metal such as steel which is cut into predetermined lengths after which the metal plate 6 of the same predetermined length is attached to the C-shaped sections as disclosed in FIG. 14.
This prior art procedure is very costly because of the handling of the parts and the separate welding which requires several operations.
The reinforcement bar of FIG. 14 also has a decided disadvantage in that a striking force applied at the edges as illustrated by arrows A and B or between the edges and web 3 causes the welded ends to be forced apart destroying the integrity of the bar.